The realization that biomechanics play a central role in understanding the etiology, treatment and prevention of injuries and pathologies of the human musculoskeletal system has led to a burgeoning interest in non-invasive, densitometric methods for assessing the structural competence of skeletal regions at high risk. Dual energy X-ray Absorptiometry (DXA) has proven to be one of the most precise and accurate of these methods, with data from our own and other laboratories demonstrating that DXA provides: 1) strong (r2=0.7 to 0.9) and highly significant associations with both clinical and ex vivo risk for age- related fractures of the hip and spine; and 2) the best available outcome measure for monitoring aging processes and the skeletal responses to interventions such as exercise and the use of osteodynamic agents. In this NCRR Shared Instrumentation Grant application, the Department of Exercise and Sport Science at Oregon State University (OSU) requests funds for the purchase of a new Hologic QDR 4500A Fan Beam X-Ray Bone Densitometer, a state-of-the-art system that provides fast (5-30 sec), fan-beam spine/hip capability in the supine position, with over four times the throughput of the QDR-1000/W system it will replace. The new system will significantly enhance and extend the reach of three NIH-funded research programs involving musculoskeletal biomechanics and tissue engineering: 1) the effects of jumping on growing bones; 2) hip fracture risk prediction by QDR; and 3) alternatives to autografts for cleft palate repair. Perhaps more importantly, this shared instrument will serve as a centerpiece for ongoing and new collaborative research efforts that will lead to an expanded focus of research in musculoskeletal biomechanics at OSU and a number of new NIH grant applications from OSU and Oregon Health Sciences University (OHSU) over the next several years.